1. Field of the Invention
The present invention relates to an electrophotograph development apparatus, more particularly to an electrophotograph development apparatus for developing an electrostatic latent image formed on an electrostatic latent image carrier body with magnetic developer.
2. Description of the Related Art
Heretofore, an electrophotograph equipment has been used for a printer, a copying machine, a facsimile and the like. As a development apparatus of this electrophotograph equipment, a development apparatus using one component magnetic developer has been used. A variety of systems have been conventionally proposed for the purpose of improving durability of the surface of a developer carrier body used in this development apparatus and an image quality. For example, the gazette of Japanese Patent Laid-Open No. Hei 7-199626 discloses a technology in which with regard to the surface roughness of a developer carrier body, JIS ten-point average roughness thereof is set to Rz 10 .mu.m or less. Moreover, a technology is disclosed, in which mixed resin including ethylene, ethyl and acrylate is added with ferrite powder, and substance thus obtained is made to serve as a dielectric layer of a developer carrier body, and average surface roughness thereof is formed to be 5 .mu.m or less, for example, in the gazette of Japanese Patent Laid-Open No. Hei 5-142938. Furthermore, a technology is disclosed, in which on the surface of a developer carrier body, an dielectric layer is formed on the surface of a thin layer forming member for forming a thin layer of developer, and surface roughness thereof is set within a range from 0.02 .mu.m to 2.mu.m, in the gazette of Japanese Patent Laid-Open No. Hei 4-086875.
An extrusion amount from a contact point of a thin layer forming member and a developer carrier body to a free edge of the thin layer forming member is illustrated in the gazette of Japanese Patent Laid-Open No. Hei 7-333984. However, a numerical value of the extrusion amount is not described here.
In the conventional electrophotograph development apparatus, even if the surface roughness Rz of the developer carrier body is set to 10 .mu.m or less, if the surface roughness Rz of the thin layer forming member is not defined, magnetic developer can not be formed into a uniformly thin layer on the developer carrier body, thus causing printing defects such as lowering of a solid black density, occurrence of a void, deterioration of density uniformity and occurrence of white base fog. As printing is repeated, the magnetic developer has been fixed to the thin layer forming member, thus causing other printing defects such as occurrence of a white stripe on a solid black surface and printed dots and occurrence of a black stripe on a white base.
Similarly, even if the surface roughness Rz of the thin layer forming member is set within the range from 0.02 .mu.m to 2 .mu.m, if the surface roughness of the developer carrier body is not defined, printing defects similar to the above-described defects occur.